The art of 2-dimensional displacement detection has long been applied in industrial controls and computer input-output peripherals. Devices incorporating this technology have become essential equipment today. The accuracy for such devices has always been a design objective. For example, in the popularized PC, the conventional key-in operation has evolved into a simpler man-machine interface, and the CURSOR control and command input is accomplished by moving the hand on a track-ball in conjunction with WINDOWS.TM. software. Besides having remarkable impact in CAD and graphic softwares, such devices have become popular in commercial, educational, household and even TV game applications. This popularity is because the devices are economical, advantageous and convenient.
Most of above-mentioned conventional devices are of the mechanical frictional transmission-type n which a moving body drives an X-axial and Y-axial ENCODER, e.g. a ROTARY ENCODER. For example, a transmission shaft is frictionized with the plate top directly, or is geared to a ball; and displacement information is encoded by an X-axial and Y-axial ENCODER. However, these conventional devices incorporate a complicated structure requiring a plurality of transmission mechanisms and rather sophisticated arrangements for the mechanisms.
Moreover, rotation results in friction, and measurement of frictional displacement inevitably causes error. Therefore, the frictional transmission type device decreases the accuracy. Furthermore, since no material is wearproof, wear and tear will increase the erroneous measurement in accordance with the amount of use. In addition, the transmission shaft or ball may carry dust and dirt from the plate surface into the internal mechanism so that routine clean-up and maintenance is necessary to prevent a complete failure of operation.
In order to solve the above-mentioned defects found in conventional devices, the inventor has developed the present invention through careful design and accumulated experience in this field, together with many experiments and improvements thereon.